Aerial Meshes

While cycling through the cornfields I recenly had an eureka moment when coming up with a really wild and crazy idea about what could be possible with underpressure based robust lighter than air metamaterial structures.

I regularly ponder about how AP technology could be applied to solve a number of problems.
The idea I had may solve at least three of them and opens up a whole bunch of other opportunities and interesting questions.

The three problems solved are:

A) The problem of keeping something stationary relative to the ground in a high up laminar large scale wind-current (e.g. CO2 collectors in the sky). This seemed to be impossible without expending energy to actively move against the current.

B) I thought about what is likely to replace today's mostly three bladed windmills that barely scratch/tap the lowest percent of the troposphere (100m of 10km). Obviously some silent sail like air accelerator/decelerator sheets/cloth/sails should become possible.
Future "power-windsails" may be quite a bit bigger than today's windmills but they still need to be linked to the ground for counter-force and counter-torque. To avoid excessively large bases advanced sail like wind generators probably would not be made excessively large (that is a large fraction of the 10km troposphere). Also giant towers permanently emanate the danger of them coming crushing down.

C) I thought about extracting the potential energy from rain-droplets: Clouldn't one look at clouds as almost everywhere available catchment lakes in the sky?

>> So here's the idea:

Specifically what came to me was to massively employ lighter than air structures in form of aerogel like "strings/filaments" (quite thick in diameter) that are tied/anchored/thethered to the ground and also intermeshed with themselves up in the sky. In the following I will refer to those structures as aerial meshes or airmeshes or airgrids. Keeping everything held at all times. This is kind of remotely similar to the principle of machine phase in the nanocosm and it too comes with a some advantages.

These structures seem to be easy to errect in giant scales. They could be applied for:
* aerial traffic
* large scale energy extraction
* and even reversely as means for super large scale strong weather control (ozone too)

Beside spanning "windsails" in the mesh loops of the "air grid" obviously "solar sails" are also possible.
Also there may be rains sails whick I'll explain later.
All sails could/should be equipped with temporary deployment capability and modes that let through part of the wind (lamellas?).

>> Wind-loads

Obviously one must worry about excessive windloads.

Even uncompensated advanced materials might be able to withstand windloads (estimations needed) the floating air strings / air filaments could be armed with a dense rope in the core. Assuming a density of 4kg/dm^3 a strong rope of about 1cm diamater needs to be embedded in an lighter than air string of at least about half a meter so that it starts floating.

To prevent getting critical loads and temporary collapse of the metamaterial due to windpressure making it temporarily non-buoyant there is the possibility of windload compensation.
Luckily with APM there's no additional cost making the whole surface an active "living" structures.
By integrating two other technologies windoads may be reducable to acceptible levels or even completely compoensatable.
Conveniently when there is windload there is also local power for the protection mechanisms.
Two main technologies usable for wind-load compensation are: (names freely invented)

A) "infinitesimalbearing parallel motionion cloaking" (this was presented by Josh Halls in his book "Nanofuture" as a means for propulsion) When air moves parallel to a surface the surface is moved with the same speed in the same direction. This replaces friction in air with much lower friction of "infinitesimal bearings" that are integrated in the air-vessels (or here air mesh strings) topmost surface layers.

B) "adiabatic normal motion cloaking"
When the aforementioned technique is used the air still needs to get out of the way sidewards of an obstacle.
While the aformentioned technology/technique can compensate for parallel air motion there still remains a motion component that is head on to the surface. Obviously this must be a motion of one period/impulse of incoming and then outgoing air in the frame of reference that is moving with the parallel motion compensation speed (I hope that formulation is sufficiently comprehensible).
What one would try here is to "grab" pockets of air compressing them down as they approach (this heats them up so they must be kept sufficiently thermally isolated to not loose their enegry) and then expanding them up again. This technique may be capable of reducing bow waves. (Though I'm rather wary about whether this could/would work or not.)

>> Robustness against lightning (and ice loads)

Obviously one must worry about lightning. There seem to be two polar opposite options.

A) Adding lightning protectors of highly conductive material. On a large scale this would probably be a bad Idea. They are likely to negatively influnece weather by quenching thunderstorms and air to ground potential in general.

B) Making the "air-strings" electrically highly isolating (not hard for an aerogel metamaterial out of high bandgap base material).
A thin layer of intermediately conducting water droplets that heats when lightning strikes (it converts to plasma and may damage the surface) may be avoidable by making the surfaces highly hydrophobic. As a nice side effect combined with small scale active surface movement this can also prevent any ice deposits and thus dangerously high ice loads.

A&B) A third option is to make the structures switchable between the two extreme states.
This may allow to extend the weather control to electric aspects of the atmosphere.

Avoiding long stretches of electrical conductors (km scale) generally seems to be a good idea.
By exclusively resorting to chemomechanical energy transmission one gets resillience against directly hitting solar storms (giant protuberances directly heading towards earth that would be devastating today due to induction of high voltages in long power lines) and maybe even even resilience against EMPs from not too near atomic blasts (that hopefully will never happen).

>> Exotic untapped energy forms:

There's a constant quite high electric field between ground and sky (aerostatic electricity).
I don't know how much energy is in there and what would happen if large fractions of this electric reservoire where to be extracted or boosted. There's some questionable science going on there with todays pretty limited technology.
Simple experiment:

A little more dangerous:

Slanted horizontal "sails" hanging below the clouds could be used like funnels guiding the rainwater to the "air-mesh-filaments" that then act like eavestroughs in the sky allowing to tap the full potential energy of rainwater. Then we wouldn't depend on a mountains with a suitable high up valley that can be blocked anymore.
Most of the rain must be redistributed at a lower level (like a shower head in the sky - rain sails ?!) to not negatively influence vegetation. Yes that sounds ridiculous but it might make sense.

>> The structure of the lifting metamaterial

For furter discussion of the limits of the technology I need to go a little more into the detail of the structure of the lifting metamaterial. These ultra light metamaterials are made out of cells with thin gas-tight walls and internal 1D trusses (possibly fractaly arranged) that prevent collapse from external pressure. Advanced surface functionalies of the airmesh strings are not located on every cell wall but on the outermost walls of a "sky string" or independent balloon. These outermost surface functionalities are not part of the base metamaterial. The "sky strings" have many basic cells throughought their diamater. The main function of the walls of each cell is just gas exclosure. This compartmentalisation that is finer grained than the whole air string gives some redundance and safety. If the metamaterial is made out of an uncombustible base material like sapphire then there is little to no chance that these structures come crushing down. Nice! The internal trusswork might be equipped with active components to adjust cell sizes a bit such that buoyancy can be adjusted. Too much buoyancy is bad too because of too much upward pulling force on the anchor points.

>> The awesome part - for nice illustrations and dreaming about the future

In some of the vertical "sky-strings" elevators could be integrated.
A (pressurised) stairway to the stratosphere would be an epic multi day climb.
Imagine the view from up there. With three point rope suspension one actually can reach any point in the sky.
Beside the view you'll get perfect silence (and quite a bit of radiation).

Climbing metamaterial "sky-strings" directly (assuming structure to grip on is made present) might feel like
like standing on a a rubber air-castle. Given too much pressure the material might temporarily collapse where you stand on / where you grip it. This quickly gets more serious with rising altitude where the metamaterial becomes less and less dense (cell size grows).

So to properly support human climbers (or other stuff like strenghtening ropes or chemomechanical power cables) proper solid structures are necessary. Albeit future devices will be very light for todays solid steel world standards these functional core structures are still heavy and dense in relation to the lifting metamaterial. So to lift the strong dense "core-structures" one has to link them to the lighter than air metamaterial. At low altitudes this might work out pretty directly (just as with current day balloons). At higher altitudes a gradient of cell size or even a fractal root net of smaller sized nonfloatong cells can softly connect to the big cells that provide negative lifting density.

>> Transportation

In a much smaller scale than for weather control air-meshes seem to be applicable for local urban aerial transport.

On regards to transport I extended on the ideas presented in Josh Halls book Nanofuture:
For reference in Nanofuture Josh Hall proposed the individualist solution without lihghter than air structures: Unthethered free moving shape shifting vessels that lift of with very very long telescoping stilts to keep downwind noise from air turbulences low. Once in the air they switch to a second sailship like mode to gain both speed and hight and once at speed they change again to a third jet like mode. He proposes "infinitesimalbearing parallel motionion cloaking". My two cents: "Adiabatic normal motion cloaking" could also be used. (I've explained both techniques above.)

I thought about replacing the scary telescoping stilt start with safer mobile lifting pillar balloons (pillar shaped to keep space on the ground) or just static cables hangig down from the air-mesh both things would be lifting gondolas up and down to and from a rail system in the airmesh thus replacing part of the local transport with very direct congestion free gondola like transport. A form of transport that is not using the inefficient method of blowing out air for lift (and propulsion) but simply reaction force on the airmesh grid.

With increasing distance it makes sense to remove the "obstacle air" altogehther.
Airmeshes allow to put horizontal vacuum pipe "railtracks" in the air where there are no hard obstacles that make speed limiting curces necessary. Superfast "airial vacuum trains" so to say. The vacume tube could be seen as a very large unsupported vacuum-cell in the core of a very fat also vacuum filled multi celled airmesh-filament structure. For longer ranges such systems are probably best situated at the lower edge of the stratosphere 10-20km to avoid weather.

The heavy passenger capsule drive system would be integrated in lighter than air metamaterial sausages of qite impressive diamater.
shorter range tracks lower in the atmosphere will need a combination of tight tiedown to the ground and dynamic windload compensation sufficient for their operation speed. Longer range faster tracks can be placed in the calmer stratosphere enclosed in even more impressively sized metamaterial sausages.

Note that in contrast to current day concepts like the hyperloop with the availability of infinitesimal bearings magnetic levitation (needing special chemical elements for the magnets) can be avoided. With the distance to the wall provided by physical contact via the infinitesimal bearings there is no rest-gas needed for air-hockey like suspension. A full vacuum is possible.

>> Interplay with existing and future air traffic:

Legacy air-traffic (old-timer historical kerosene driven noisemakers) should still be able to fly by sight.
Airmeshes designers must consider that in their plans too. This may come in conflict with the desire to keep the looks of the landscape pristine for human eyes (optical cloaking).
It is difficult to guess how much "air filaments" will be visible when designers just does not care about the looks.
Likely appearances may be: transparent, milky, iridescent - like deep sea creatures ??

There could be constantly open flight corridors in the mesh or the mesh could dynamical open op windsails so that vessels can move through. The sails should be able to detect punctual non wind like force and rupture in a controled reversible fashion when a plane or a bird crashes into them.

>> anchoring density an anchoring pattern

There are a lot of questions:
* What would be the most practical end aesthetical mehing pattern (foam edges?)
* What would be a good density of anchoring points on the ground in cities and on land?
* How would one do the anchoring of an airmesh on sea?
* What do one end up if the mesh cocept is applied to other "XYZ-spheres" (Hydrosphere, Lithosphere, Biosphere, ...)?

With the capability to lift stuff high enough one could e.g. start thinking on raising the linear rail acceleration vacuum train speed to a level where it essentially becomes a propellant-less direct in orbit injection space launch systems. The space vessel is released into the atmosphere where the density is low enough such that the deceleration shock is low enough to not damage or destroy the cargo. More on that later.

So what is the limit? This seems to be a rather hard to answer question.
Under the assumption that with fractal truss frameworks for cell inflation buckling instabilities can be avoided scaling seems to imply that by simply keeping the mass of the internal structure of the metamaterial cells constant but spreading out the volume one can keep up with the falling density of air while also keeping up being capable of compemsating the external pressure.

With rising volume the mass of the super thin sealing surfaces does not loose relevance. While both the mass of the displaced gas such as the mass of the outward pushing truss structure in a cell stays the same with growing volume the surface area is rising. So either it is made thinner or lifting capacity will decline. (more analysis needed)

At some point one ends up with e.g. long trusses of single walled nanotubes (or fireproof sapphire rods) that become wobly only due to thermal vibrations alone. Or with single sheets of graphene as walls. But long before that destructive environmental factors ("forces of nature") may put a stop to ambitions.
(Here I'd like to ask readers to please check this rough train of thought on major mistakes)

Todays helium balloons do hit a wall at about 50km hight. They use about ~3000nm thick plastic film.
Jaxa: global.jaxa.jp/article/interview/vol42/p2_e.html
By replacing the helium fill with the most part of the shell thickness converted to internal fractal trusswork structures that resist the now occuring external pressure against the inernal vacuum one gets rid of the problem of varying internal pressure due to day night temperature variations. The other way around keeping the hight constant while the external pressure will roughly stay the same the external air density will somewhat vary with day and night - that seems less problematic.

As a rule of thumb the air pressure in earths atmosphere halves with every 5.5km hight.
Thus compressed down to 1bar in hypothetical weightless sapce the whole atmosphere would be about 11km thick.
With a few exceptions it is probably impractical to put any major weight carrying stuff much above that height mark.
Being high enough to be above the most part of the weather acticity (bottommost part of the stratosphere - like planes) may be beneficial for some applications.

>> Propellant-less space launch system ??

Such a thing would be a pretty dense and heavy very long perfectly circular (earth radius) tube floating at a hight where the atmospheric density is low enough that the deceleration shock on release into the atmosphere is less than 10g (How to calculate this hight for e.g. LEO speed(~8km/s) and escape speed(~11km/s)?).

Josh Hall proposes a sequence of 80km high towers (mesopause - coldest point in the atmosphere -100°C) holding such a space launch system up. (It's rather scary imagining them crushing down). But is the pressure at 80km low enough to allow direct orbilal launch?

A circumglobal mesosphere to thermosphere space launch corridor would even if the mass per length is kept as minimal as possible have to have a buoyancy providing enclosing lifting device of imposing diamaeter (estimated minim um at 80km: ~2km for 100kg/m; ~5km for 1000kg/m ?). This is starting to reach down into the denser parts of the atmosphere making it more like a ship swimming on the atmosphere.

The lifting device for such a system of course would be ridiculously filigree. Its not unlikely that such ambitions will be thwarted by UV damage or micrometeorites. Wikipedia says: "The lower stratosphere receives very little UVC" but here we are higher than the ozone layer (average height of ozone layer: 15-20km tropes 20-30km - btw: stratospheric airmeshes could be used to replenish or further fortify the ozone layer) UV-B and UV-A comes through anyway. The one thing that's unproblematic is the massive availability of space precisely because nothing else is capable of staying stationary at these heights.

As long as one does not get too far into the overpressure regime (limiting today's balloons) one may be able to extend the height limit a bit by more conventionally using a bit of lifting gasses to help. There's plenty of hydrogen available but in an oxygen rich atmosphere even when enclosed in a fireproof metamaterial this seems unsafe (true?). Both Helium and Neon are rather rather rare. It would take much time and energy to concentrate them up for lifting bigger stuff like a space launch system.
In a hyper long term perspective one could say that concentrating up all the light noble gasses of our atmosphere is good idea since it keeps them from further depletion to outer space. About light noble gasses as a space resource could be speculated but the solar systems major helium depos Uranus and Neptune seem to have too deep gravity wells to send out anything but photons.
Placing a vacuum balloon space launch system on Uranus or Neptune would be even more challenging due to their lightweight hydrogen atmosphere.

As mentioned before to lift a dense and heavy objects to great heights a continuous gradient to lower density material is necessary.
thermospheric Space launch systems would take that to the extreme.

>> Conclusion

As you see the amount of possibilities with this kind of technology would be enormous.